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Go Back   SailNet Community > On Board > Gear & Maintenance > Impeller replaced, but did I screw up?
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Thread: Impeller replaced, but did I screw up? Reply to Thread
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Topic Review (Newest First)
02-24-2010 07:50 PM
countrygent5201 Wow, this has been the most helpful experiences I've had on an Internet forum. I think I finally understand how my cooling system works. The raw water does the same thing in the heat exchanger that air does in a radiator -- remove heat from the primary coolant. I can't thank you guys enough for all your help. You've saved me not only untold hours of work, but possibly some big bucks in engine repairs if you had not encouraged me to go looking for the missing impeller vanes. And I am SO happy that I don't have to waste the next week searching for zincs that don't exist on my engine. All of you have been very generous with your knowledge, and for that I am extremely impressed and grateful.
02-24-2010 07:11 PM
JohnRPollard
Quote:
Originally Posted by GeorgeB View Post
....The engine’s zinc is mounted in the “outside water” side of the exchanger. If you have a heat exchanger, you have a zinc. Look for a brass bolt head mounted on the bottom side of exchanger where the sea (outside the boat) water comes in. Chances are when you remove the brass bolt head, you won’t see a zinc as it has completely dissolved some time ago. What is your engine's operating temperature? It should be around 160 – 165 degrees, 180 max. If it is over this this, you need to take out your exchanger and clean it out (you can go to a radiator shop for this). If you are around 180, you should still clean it, but it is not yet mission critical.

For those of you that don’t have a heat exchanger, you still have a zinc mounted somewhere. Consult your engine’s manual. Getting a heat exchanger re-cored is easy, re-coring an engine block is hard. That’s why most boats have heat exchangers.
George,

The Yanmar 2GM20F and 3GM30F do not have engine or heat exchanger zincs. I've owned both and never changed a zinc.

The heat exchangers were made with an alloy that does not require them (copper nickel, think).

We have some threads on this, let me see if I can find some... here we go:

http://www.sailnet.com/forums/gear-m...ar-3gm30f.html

http://www.sailnet.com/forums/diesel...ar-20m20f.html
02-24-2010 05:08 PM
GeorgeB The vast, vast majority of sailboats have a two loop cooling system. The primary loop circulates water/coolant through the engine block and is moved by the metal water pump mounted on the front of the engine block. This water/coolant circulates on the primary side of the heat exchanger (think car’s radiator). The secondary loop takes water from the outside of the boat and flows it through the heat exchanger. This water is moved by the bolted on water pump that you replaced the rubber impeller on. The engine’s zinc is mounted in the “outside water” side of the exchanger. If you have a heat exchanger, you have a zinc. Look for a brass bolt head mounted on the bottom side of exchanger where the sea (outside the boat) water comes in. Chances are when you remove the brass bolt head, you won’t see a zinc as it has completely dissolved some time ago. What is your engine's operating temperature? It should be around 160 – 165 degrees, 180 max. If it is over this this, you need to take out your exchanger and clean it out (you can go to a radiator shop for this). If you are around 180, you should still clean it, but it is not yet mission critical.

For those of you that don’t have a heat exchanger, you still have a zinc mounted somewhere. Consult your engine’s manual. Getting a heat exchanger re-cored is easy, re-coring an engine block is hard. That’s why most boats have heat exchangers.
02-24-2010 05:06 PM
redhead78 Gent, to put it so you may understand better, look at the freshwater system you have like a car. You do have a sealed section in your engine block where you have anti freeze flowing thru just like your car, that helps remove the heat from the engine. Your car has a radiator to remove the heat from the coolant, your boat has the lake. The raw water we speak of is pumped thru the heat exchanger via the said impeller you are working on.The anti freeze runs thru a series of baffles, in the "heat exchanger" (thus the name) that are surrounded by the cool lake water which removes the heat from the anti freeze. This kind of system is good because any crap in the water that is not caught by your water filtration system(probably deserves a peek also) does not enter the engine itself. The heat exchanger can be taken apart and cleaned. sorry for being so wordy.....Red
02-24-2010 04:04 PM
JohnRPollard
Quote:
Originally Posted by countrygent5201 View Post
Actually, my Yanmar has both a raw water cooling system and a fresh water system. I don't know how they work together, but there are two separate systems -- one that pumps water from the lake, through the engine, then back into the lake, and a closed system that's filled with diluted antifreeze, including an overflow tank like we have on our cars. If anyone knows why there are two cooling systems on the Yanmar 2GM20(F), I'd sure like to know.

I've also been thinking about the zincs. I'm sure they need replacing, but I have no idea where to look for them or what they look like. The diagram in the Yanmar manual shows the location as somewhere near the back of the engine, but doesn't show an upclose image so that I would know what to look for. Is it something that screws into the engine? Would I have to go to Yanmar for a replacement or is this something I could get at a place like West Marine?
The cooling system you describe is referred to as a "fresh water cooled" system. This means your engine is fitted with a heat exchanger and antifreeze reserve.

Yes, there is a "raw water" part of your system, but to avoid confusion, we call your system "fresh water cooled". A system that lacks the heat exchanger is called "raw water cooled".

In other words, when you say that you have a "fresh water cooled" engine, it is taken for granted that there is a raw water component to that.

To the best of my knowledge, the fresh water cooled Yanmar 2GM20F does not have engine zincs.

P.S. Good job on the impeller retrieval!
02-24-2010 03:59 PM
sailingdog Nicely done...
Quote:
Originally Posted by countrygent5201 View Post
Yippee!!!

Went back to the boat this am to try to solve the mystery of the four missing impeller vanes. Pulled the hose between the pump and heat exchanger (I think that's what it is) and found one firmly lodged against the barb. Found two more inside the hose. Stuck a wire into the exchanger a few inches and felt something soft. Bent a small hook onto the end of the wire and, after about 10 minutes, fished the last one out of the exchanger itself. All four accounted for! Thanks to all for your help and comments.
02-24-2010 03:55 PM
countrygent5201 Actually, my Yanmar has both a raw water cooling system and a fresh water system. I don't know how they work together, but there are two separate systems -- one that pumps water from the lake, through the engine, then back into the lake, and a closed system that's filled with diluted antifreeze, including an overflow tank like we have on our cars. If anyone knows why there are two cooling systems on the Yanmar 2GM20(F), I'd sure like to know.

I've also been thinking about the zincs. I'm sure they need replacing, but I have no idea where to look for them or what they look like. The diagram in the Yanmar manual shows the location as somewhere near the back of the engine, but doesn't show an upclose image so that I would know what to look for. Is it something that screws into the engine? Would I have to go to Yanmar for a replacement or is this something I could get at a place like West Marine?
02-24-2010 03:39 PM
countrygent5201 Yippee!!!

Went back to the boat this am to try to solve the mystery of the four missing impeller vanes. Pulled the hose between the pump and heat exchanger (I think that's what it is) and found one firmly lodged against the barb. Found two more inside the hose. Stuck a wire into the exchanger a few inches and felt something soft. Bent a small hook onto the end of the wire and, after about 10 minutes, fished the last one out of the exchanger itself. All four accounted for! Thanks to all for your help and comments.
02-24-2010 10:39 AM
sailingdog The lack of grease shouldn't be an issue as long as you've got water flowing into the system. The missing blades are likely stuck in the heat exchanger, and if you haven't taken that apart and cleaned it out, it is probably past due for it. It'll probably have bits of old zincs too. Speaking of zincs, have you replaced the zincs in the engine?
02-24-2010 09:55 AM
JohnRPollard
Quote:
Originally Posted by countrygent5201 View Post
Took another look at the diagram and I am obviously wrong about how the raw water system works. I'll check the lines at the first opportunity and hopefully will find the missing vanes.
Yeah, it pushes the water through, not pulls it.

Back to your original questions:

There's no issue with the impeller and the lack of grease. The boat is just sitting there with the engine off. In fact, I don't even put grease on the impeller blades and have never had an issue (I do occasionally run just a very thin amount of grease around the inside of the impeller chamber, but not every time).

As for the old impeller blades... A bit of a quandary there. They could have broken off intact, or given how old it was they might have even slowly disintegrated in small bits. I don't think anyone can tell you for sure because I don't think anyone has run an impeller that long! (Actually, I'm skeptical that it was NEVER replaced. Maybe a mechanic took care of it and the previous owner wasn't savvy enough to follow along).

But you haven't said whether your engine is raw water or fresh water cooled (someone else did, but I'm not sure how they reached that conclusion). A "raw water cooled" engine does not have a heat exchanger with anti-freeze reserve. Instead it just pulls raw water from outside the boat and pushes it through the cooling veins of the engine. A "fresh water cooled" boat has a heat exchanger with antifreeze reserve, and simply uses the raw water to cool the heat exchanger.

So the path you have to follow is different depending on what kind of cooling system you have.

For those from the "south" wondering why he'd be discharging anti-freeze, either system is winterized against freezing damage by running non-toxic antifreeze through the "raw water" portion of the cooling system. This gets mixed with and discharged out the exhaust tube.
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